In cutting teeth during dental treatment, water is sprayed onto the cutting site for reducing friction resistance between the cutting tip and teeth or removing debris. Water is also used for rinsing oral cavity during dental treatment, or washing treatment site with water spray. Water used for such purposes is usually tap water, which is relatively cold. Thus when the water gets into the treatment site or decayed teeth, the patient may feel pain.
In order to solve this problem, water heaters are used for warming water before use. However, conventional water heaters are relatively large or require a large space for installment. Some heaters are even insufficient in heat efficiency in warming water.